1. Field of the Invention
The invention relates to a method for drying slurry, which in a living quarters for animals such as agricultural livestock is produced by these animals, or rinse water or industrial effluent and/or residues, which method comprises the steps of:
providing an air-permeable drying bed with suitable carrier material;
arranging, for instance spraying, the slurry on the drying bed;
drawing in and/or blowing drying air and guiding this air through the drying bed;
removing thus dried manure; and
shuffling the carrier material at chosen times, for instance periodically, in order to ensure a predetermined air-permeability of the drying bed.
2. Description of the Related Art
According to known methods for drying slurry the slurry is first of all separated into a thin and a thick fraction, whereafter the thick fraction is dried while the thin fraction is disposed of. A drawback hereof is that a large part of precisely those minerals which can serve as nutrients for plants are dissolved in the thin fraction.
U.S. Pat. No. 5,666,905 describes a method wherein slurry drops through a slatted floor into a basement and there has the water removed with drains. Air from the living quarters is blown through and over the drained thick fraction in order to dry the manure.
A drawback of this method is that the manure is drained, whereby the manure is separated into a watery and a thick fraction. Only the thick fraction is dried and the thin fraction is disposed of. Since the manure accumulates in the basement, the air permeability is very poor, whereby it is necessary to apply a forced air flow for which a relatively large amount of energy is required to overcome the air resistance.
An additional drawback of the device described in U.S. Pat. No. 5,666,905 is that the space in which the manure is dried extends below the whole living quarters. The construction hereof entails extra cost.
U.S. Pat. No. 4,706,607 describes a device and method for drying manure. The slurry herein drops through a slatted floor into a basement in which a thick layer of sawdust is arranged. A shuffler is arranged to periodically shuffle the slurry and sawdust.
The sawdust has the purpose of absorbing the slurry. Air is introduced into the mixture of slurry and sawdust by the shuffling process in order to enhance the aerobic fermentation. Stated as option is to aerate the bottom part of the sawdust with an xe2x80x9cair blowout pipelinexe2x80x9d. The air serves for the composting process and not for the purpose of drying. The drawback of this process is that the end product consists largely of sawdust, so that the mineral concentration is low. The amount of waste material is not reduced by adding the sawdust. The end product is moreover not really dried. A compost product is made.
The invention has for its object to prevent the above stated drawbacks and to provide a system which dries slurry to a form in which it can be disposed of without adverse consequences and wherein the emission of harmful substances, such as for instance ammonia gas, is reduced. All minerals are also preserved in the dried end product.
This objective is achieved according to the invention by a method which is characterized by
measuring quantities of the drying air;
measuring quantities of air guided through the drying bed; and
arranging the slurry, shuffling the carrier material and removing dried manure (or the dried industrial residual product or waste flow) on the basis of the measured quantities.
Measuring of the different quantities and performing the different steps on the basis thereof enables precise control of the process, whereby a minimal amount of energy is used to obtain a maximum result. These quantities are for instance the flow rate, temperature and air humidity of the air flow.
Use can be made in advantageous manner of the ventilation air of the living quarters. This air has an air humidity of around 80%. This stall air is usually preheated. Another advantage of using stall air is that it is ventilated in very large quantities.
In addition, the dust is filtered out of the is stall air by the device, so that it can be disposed of with the dried manure.
According to a further embodiment of the method according to the invention the method comprises the step prior to performing step (B) of adding an additive, such as a bacteria culture, to the slurry. The addition of an additive, for instance a bacteria culture, makes it possible to accelerate the decomposition of (harmful) substances, whereby the emission of for instance dust, ammonia and odour can be reduced. A chemical substance can also be envisaged as additive, whereby for instance the acidity of the slurry can be increased or decreased, or a vegetable substance which for instance dispels odour.
The invention further comprises a device for performing the method according to the invention, which device comprises:
a housing;
an air-permeable drying bed with suitable carrier material arranged in the housing;
application means arranged in the housing and placed above the drying bed for distributing slurry over the drying bed;
ventilation means for drawing in air from the living quarters and guiding the air through the drying bed; and
removing means for removing a layer of thus dried manure (or other dried product).
In a preferred embodiment of a device according to the invention, this device comprises a shuffler device for shuffling the dried slurry on the drying bed in order to ensure a predetermined air-permeability. The thickness of the drying bed is preferably kept as small as possible, for instance a thickness of 3-10 cm. The pressure losses over the drying bed are kept minimal by the shuffling, whereby operation can usually take place with the existing ventilators of the living quarters (or, in the case of industrial applications, the factory). No additional energy, or only a minimal amount, is then necessary to guide the air through the drying bed. At start-up a carrier material other than the product for drying is usually used temporarily (for instance a compost-like product). The shuffler device can be embodied such that it also form the removing means for removal of a layer of manure.
In yet another preferred embodiment of the device according to the invention, the device comprises a reservoir for storing the slurry; and means for mixing the manure in the reservoir in order to obtain a substantially homogeneous mixture. When the slurry is pumped out of the manure pit, it is then not completely homogenous. So as to allow spraying and/or distribution of the slurry to take place optimally and to prevent fouling or blockage of the sprayers, the slurry is stored temporarily in a reservoir and there homogenized by means of homogenizing means such that an improved homogeneity results.
The housing of the device is preferably formed by a container of standardized dimensions. It is hereby possible to construct the system in the container and to transport the whole container, including the device, to an existing living quarters and there connect it to the air extraction. Another advantage of a container is that it is readily insulated, whereby little heat is lost. A separate space in a living quarters or in an area of a living quarters can for instance also serve as housing.
In a further preferred embodiment of the device a heat exchanger is connected onto the outlet of the ventilation means with which fresh air carried into the living quarters can be heated with the used air from the living quarters.